1. Field of the Invention
The present invention relates to zoom lenses and, more particularly, to a zoom lens having a diffractive optical element which is suited to lens-shutter cameras, video cameras, or like optical apparatuses.
2. Description of Related Art
For the lens-shutter camera or the like that does not require the long back focal distance, many zoom lenses so far proposed are of the type comprising, in order from an object side, a first lens unit of positive refractive power and a second lens unit of negative refractive power, wherein the air separation between these two lenses is varied to effect zooming.
Also, in Japanese Laid-Open Patent Applications No. Sho 56-128911, No. Sho 57-201213, No. Sho 60-170816, No. Sho 60-191216 (U.S. Pat. No. 4,659,186), No. Sho 62-56917, etc., zoom lenses which are improved to a compact form have been proposed each comprising, in order from an object side, a first lens unit of positive refractive power and a second lens unit of negative refractive power, wherein the separation between these two lens units is varied to effect zooming. As these zoom lenses employ the plus-minus refractive power arrangement in this order from the object side, the back focal distance is made relatively short. Moreover, the physical length for the telephoto end of the complete lens is shortened, while still maintaining realization of a high optical performance.
Further, as derived from the 2-unit zoom lens by dividing the first lens unit of positive refractive power into two parts of positive refractive powers, another type of zoom lens is obtained. That is, a zoom lens is constructed from three lens units in total and has a plus-plus-minus refractive power arrangement, whereby the action of varying the focal length is laid on the second and third lens units to assure a great increase of the zoom ratio. Such a 3-unit zoom lens has been proposed in, for example, Japanese Laid-Open Patent Applications No. Hei 3-282409, No. Hei 4-37810, No. Hei 4-76511, No. Hei 4-223419, No. Hei 5-264903, etc.
In the meantime, for the purpose of facilitating the correction of chromatic aberrations, it is known to provide part of an optical system with a diffractive optical element, as disclosed in Japanese Laid-Open Patent Applications No. Hei 4-213421 (U.S. Pat. No. 5,044,706), No. Hei 6-324262, No. Hei 9-19273 and No. Hei 9-19274.
It is an object of the invention to provide a compact zoom lens having good optical performance. In particular, a good stability of the correction of chromatic aberrations has to be maintained throughout the entire zooming range. It is, therefore, another object of the invention to provide a zoom lens having a diffractive optical element of heretofore unknown form.
To attain the above objects, in accordance with an aspect of the invention, there is provided a zoom lens which comprises, in order from an object side, a first lens unit of positive refractive power, a second lens unit of positive refractive power and a third lens unit of negative refractive power, wherein the first, second and third lens units are moved such that, during zooming from a wide-angle end to a telephoto end, a separation between the first lens unit and the second lens unit increases and a separation between the second lens unit and the third lens unit decreases, and wherein the zoom lens has a diffractive optical element.
In accordance with another aspect of the invention, there is provided a zoom lens which comprises, in order from an object side, a first lens unit of positive refractive power and a second lens unit of negative refractive power, wherein an air separation between the first lens unit and the second lens unit is varied to effect zooming, and wherein the first lens unit includes at least three lenses and the first lens unit has a diffractive optical element.
In accordance with a further aspect of the invention, there is provided a zoom lens which comprises, in order from an object side to an image side, a first lens unit of positive refractive power and a second lens unit of negative refractive power, wherein an air separation between the first lens unit and the second lens unit is varied to effect zooming, and wherein the first lens unit has a positive lens disposed closest to the object side and a negative lens disposed closer to the image side than the positive lens, and the zoom lens has a diffractive optical element.
In accordance with a further aspect of the invention, there is provided a zoom lens which comprises, in order from an object side, a first lens unit of positive refractive power and a second lens unit of negative refractive power, wherein an air separation between the first lens unit and the second lens unit is varied to effect zooming, and wherein the first lens unit has two positive lenses and two negative lenses and the first lens unit has a diffractive optical element.
In accordance with a further aspect of the invention, there is provided a zoom lens which comprises, in order from an object side, a first lens unit of positive refractive power and a second lens unit of negative refractive power, wherein an air separation between the first lens unit and the second lens unit is varied to effect zooming, and wherein the first lens unit has one positive lens and two negative lenses, and the first lens unit has a diffractive optical element.
In accordance with a further aspect of the invention, there is provided a zoom lens which comprises, in order from an object side to an image side, a first lens unit of positive refractive power and a second lens unit of negative refractive power, wherein an air separation between the first lens unit and the second lens unit is varied to effect zooming, and wherein a stop is disposed within the first lens unit and, when the first lens unit is divided into a front lens sub-unit closer to the object side than the stop and a rear lens sub-unit disposed closer to the image side than the stop, the rear lens sub-unit has a diffractive optical element.
These and further objects and aspects of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.